Presently, with the progress of biotechnology, the research of biological sensing becomes increasingly diversified. For example, the understanding of the characteristics such as DNA, RNA, enzymes and other proteins has a great benefit to biotechnology or medicine.
In current research of biological sensing system, many people focus on the changes between the characteristics of a biological sensing unit before and after various biological molecules are bound to the biological sensing unit, for example, the change in the optical characteristics of a biological sensing unit after an antibody, an antigen, or a DNA is bound to the corresponding antigen-, antibody- or DNA-functionalized biological sensing unit. In a method for measuring optical characteristics, light emitted from a light emitting diode or a laser can be used to interact with a biological sensing system and measurement is made for intensity changes or wavelength changes in the light after the interaction to estimate characteristics of biological samples. A method for measuring wavelength changes requires a bulky spectrometer, which is inconvenient to carry around and costly. A photo detection unit with a smaller volume and lower costs can be used in measuring changes in light intensity. The development of modern biological sensing is moving toward the trend of miniaturization. If the sensing method and operating performance of a biological sensing system can be designed simpler and more convenient to carry around for sensing purposes, the sensor will be greatly applicable.
In recent years the development of nano materials increasingly becomes a focus of research, and the industries such as optoelectronics, communications and medical instruments spend a lot of effort on the research and application of nano materials. Nano materials are so favored because nano materials provide properties completely different from the characteristics of the original materials. A free electron cloud on a noble metal nanoparticle surface is excited by an electromagnetic field with a specific frequency to produce a collective dipole resonance, but the oscillating electron cloud is restricted in the neighborhood of the nanoparticle, and thus such a resonance is called localized plasmon resonance (LPR). It is interesting to find that if the environmental refractive index around the noble metal nanoparticle changes, the frequency and the extinction cross-section of the LPR band will change accordingly. If the environmental refractive index around the noble metal nanoparticle increases, the localized plasmon resonance absorption band will shift to a longer wavelength and the absorption cross-section of the LPR band will increase. While observing the characteristics of scattered light, it can be found that when the environmental refractive index rises, the localized plasmon resonance scattering band also shifts to a longer wavelength and accompanied with an increase in the light intensity. Finally, modification is made for a specific recognition unit to provide a specific sensing ability. After the relationship between changes in the frequency or changes in the extinction cross-section of the resonance band and the concentrations of an analyte is analyzed, a calibration method is established. To enhance the change, noble metal nanoparticles are modified on an optical fiber to form a noble metal nanoparticle layer in this method. The above-mentioned noble metal nanoparticle layer is composed of one of noble metal nanospheres, noble metal nanosquares, noble metal nanocones, noble metal nanorods and noble metal nanoshells. Basically, the nanoparticles are not connected with each other. The noble metal is gold, silver or platinum. The characteristic that multiple total internal reflections take place in the optical waveguide is used to accumulate evanescent-wave absorption by the plasmon resonance of the noble metal nanoparticles, so as to enhance LPR signals and improve the sensing sensitivity. The sensing element developed by the combination of the optical waveguide substrate and the localized plasmon resonance principle, as described above, is called an optical waveguide-localized plasmon resonance (OW-LPR) sensor. If an optical fiber is used as the optical waveguide component, it is called a fiber optic-localized plasmon resonance (FO-LPR) sensor. If a tubular waveguide is used as the optical waveguide component, it is called a tubular waveguide-localized plasmon resonance (TW-LPR) sensor. If a planar waveguide is used as the optical waveguide component, it is called a planar waveguide-localized plasmon resonance (PW-LPR) sensor. After integration with a molecular or biological recognition unit, it has a sensing ability with high specificity and high sensitivity, so it has great potential to be developed as a sensing device for real-time detection.
Referring to FIG. 1, there is shown a schematic view of a prior art fiber optic-localized plasmon resonance biological sensing system. Light emitted from a light emitting diode or a laser B that is driven by a function generator A passes through a sensing optical fiber in a microfluidic component C, then the photodiode detector D receives and converts the passing light into an electric signal, which is sent to a lock-in amplifier E for analysis and demodulation, and then the computer F system displays the result after demodulation and analysis. However, due to the physical characteristics of light emitting diodes or lasers (including laser diodes), the intensity of light outputted from the light emitting diode or laser changes with age or difference in environmental temperature after being used for a period of time. Therefore, it is often unable to distinguish whether a signal change is caused by a is characteristic of a sample in the microfluidic component or by a change in the intensity of light outputted from the light-emitting unit itself during the detection. If light emitting diodes or lasers of special specifications and photoreceivers of special specifications are used, it is costly, complicated in operation and bulky in volume so that the cost of a biological sensing optical measuring system is significantly increased or it is difficult to miniaturize such system. Hence, the inventors design the photoelectrical feedback sensing system to improve the stability of a light emitting source.